The synthesis, characterization and chemistry of novel η3-allyl metal complexes (M = Ir, Rh) are described. The structures of compounds (C5Me4H)Ir(PPh3)Cl2 (1), (C5Me4H)Ir(PPh3)(η3-1-methylallyl)Br (3a), (C5Me4H)Ir(η4-1,3,5-hexatriene) (8), and (C5Me5)Rh(η3-1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed. It is found that the neutral metal allylic complex [Cp*IrCl(η3-methylallyl)] (5) ionizes in polar solvents to give [Cp*Ir(η3-methylallyl)]+Cl- (6) and reaches equilibrium (5 ⇌ 6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such as [Cp*Ir(η3-methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain, temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes. © 2007 Elsevier B.V. All rights reserved.